So, what are Bug-types, really?
The Purpose of the Bug Type:
As said before, Bug-type was created as a classification type for arthropod-based species in Pokémon. These species were supposed to be some of the earliest Pokémon you could encounter and evolve, and eventually dispose of. Bug-type, like Grass-type, was designed to be gotten rid of later. To make it not too unbalanced for the type however the type was granted to major capabilities. One was defensive, it was granted resistance to two of the most common and powerful offensive types, Fighting and Ground. However, these were also granted for Flying-type and Grass and Psychic generally got around Fighting and Ground respectively through other means. This role was later disposed of by Dark and Fairy-types, who dealt with Psychic and Fighting-types.
Though Bug-type tried to get out of its classification status and become a more common type it was largely hit and miss. First major attempt was at Generation II, where an arachnid became a Bug-type. Second was in Generation III, where Signal Beam was designed to have a more digital look, and this idea was later alluded to in Pattern Bush in Sevii Islands, a location which was based off an integrated circuit board. Another major attempt was at Gen V, where a snail, Shelmet, and a crustacean, Dwebble were both in Bug-type. These are too few to make anything out of it, though.
The Aesthetic Archetypes of Bug Types:
Almost all Bug-types are arthropods. Species that are arthropod-based but not insects are allowed to be in the type. Bug-type comes in primarily Green, Blue and Red colors, with some being Yellow. Aesthetically, they can be divided into following groups:
Species that have a full three stage lifecycle, Cocoons are species that start off at a grub form, then pupate into a cocoon and finally evolve. Most of them are butterfly and moth based and thus get Quiver Dance, but this is not an absolute.
Species that are generally two staged, they start off at a baby stage and then evolve into a dog-sized spider. They get access to Spider Web and Sticky Web.
Unlike their cocoon counterparts, these are species that a grub that might be unrelated to the final evolution. They don't pupate but evolve something close to a moth or butterfly.
Physically offensive species with affinity towards Fighting-type moves, they are generally one staged though one of them is two staged.
Note: Grubbin is technically a beetle, but it belongs to the Cocoon archetype.
The In-game Archetypes of Bug Types:
Early Bug-type: The primary Bug-type archetype. They are generally cocoons. They can be either in 395-415 range or 485-500 BST range.
Secondary early Bug-type: Generally stronger than the conventional early Bug-type, these are more gimmicky species that are bit harder to obtain. They are in 450-470 range and they tend to be two staged.
Mid-game Bug-type: Later game Bug-types, these are much stronger Bug-types in around 500 range. They are supposed to be replacements to your early Bugs, but sometimes the two species can be unrelated, giving them reason to coexist.
Late-game Bug-type: A fairly rare variant of mid-game Bug, these are Bug-types you encounter during the last legs of your adventure. They are quite powerful, but they tend to have a crippling weakness.
The Stat Archetypes for Bug Types:
Quiver Dance: Species that excel in Special offense, defense and speed, these species exist primarily for Quiver Dance, even if they don't get the move. They are generally terrible or mediocre.
Fast Offense: Species with good offense and Speed, and some okayish defense, they are about dishing as much as damage as quickly as possible. They are generally not powerful enough to be considered true sweepers.
Brick Wall: Defensive species with utility moves, they generally serve for set up and using moves like Counter and Mirror Coat. They generally have low health and no recovery.
Bulky Offense: Conventional bulky offense. Bug-types are generally weak in the opposite direction of their offensive capabilities.
Annoyer: Fast species with status spam, or some other support means, they generally use their speed to cripple the opponent.